In a bowl, mix flour, salt, and sugar. Cut in butter until crumbly.
Add ice water gradually, mixing until dough comes together.
Shape dough into a disk, wrap, and chill for 30 minutes.
Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.
In a separate bowl, toss strawberries, blueberries, sugar, lemon zest, and cornstarch.
Roll out dough and cut into 4–6 small circles.
Place fruit filling in the center of each circle.
Fold edges over slightly, leaving the center exposed.
Brush edges with egg wash and sprinkle with coarse sugar.
Bake for 25–30 minutes until golden brown and bubbly.
Cool slightly before serving.